With iOS 7 you can simply change tintColor property of the UITextField. This will affect both the color of the text cursor and the text selection highlight color.
You can do this in code …
textField.tintColor = [UIColor redColor];
…
In Swift 4:
textField.tintColor = UIColor.red
…or in Interface Builder:

You can also do this for all text fields in your app using the UITextField appearance proxy:
[[UITextField appearance] setTintColor:[UIColor redColor]];
In Swift 4:
UITextField.appearance().tintColor = UIColor.red
Below are simulator screenshots showing what an otherwise ordinary iOS 7 text field looks like with its tint set to red.
Text cursor screenshot:

Text selection screenshot:
